The present invention relates to seals, and more particularly pertains to a unitized radial and facial seal intended principally for use between radially inner and outer relatively rotationally and axially movable members.
There are numerous applications in which relatively rotating members require a seal or seals to retain lubricant and exclude contaminants. Sealing a shaft in a contaminated environment while the shaft is simultaneously rotating and undergoing axial reciprocation represents a very difficult sealing problem. Conventional rotary shaft seal designs include lips intended to run on a very thin surface lubricant film on a rotating shaft. Failure or absence of the lubricant film results in high friction and attendant rapid wear of the sealing lip. Accordingly, in a rotating application, the force used to bias the sealing lip against the shaft should not therefore be so great as to cause the seal lip to break through the lubricant barrier which "wets" or adheres to the shaft surface. Due to the relatively low seal-to-shaft bias force, a seal designed to operate in a rotary application will fail in an axial reciprocating application because lubricating oil will bypass the sealing lip as the shaft moves axially. When the shaft moves to an axially extended position, contaminants will collect on the surface of the shaft. Subsequently axial retraction of the shaft tends to force the collected contaminants into the seal lip. The very fine and typically abrasive contaminant particles will pass under the seal lip because the seal-to-shaft bias force is not sufficient to break through the lubricant film. The contaminant particles will abrade both the sealing lip and the shaft and over time the shaft will become scored, resulting in lubricant leakage.
For these reasons, it is desirable in simultaneous rotational and axially reciprocating shaft applications to provide for a facial sealing lip to exclude contaminants and prevent such contaminants from coming into contact with the radial sealing lip. Wide linear manufacturing and assembly tolerances can, however, cause difficulty in determining the exact linear position on a shaft for installation of a facial seal to ensure positive, uniform contact between the facial seal and a mating surface to be sealed.